Where possible I would avoid using POP3 accounts. My host allowed me to upgrade to IMAP and it is so much easier. I think the only way to accurately create any form of mail client with POP3 is to download the messages into an SQL database which is a big task to start with, considering the IMAP standards have the functionality we need built in.I experimented with flag setting in POP3 and it seems they do not stick at all, and it is almost impossible to retrieve the number of unread messages (ie. the Seen / Unseen thing does not work)Converted to IMAP and it's working - the majority of the functions in this section seem to be IMAP focussed and WILL NOT generally work with POP3

Indeed POP3 does not support flags that indicate the "newness" of a message. There are other ways to work around this problem, though. For one, I have seen mail delivery systems that will add a header field Status: to indicate its status (see RFC2076). Another way most email clients and mail fetching programs seem to use is to keep a local list of UID's of messages that are downloaded. Upon fetching mail, the UID's of the messages can be checked against this list to see if it was already downloaded. POP3 supports a command UIDL to get a list of all UID's, but I doubt the IMAP lib uses this command. The only thing I know of that will thrash this work-around is the use of multiple mail clients. If another mail client fetches mail from the server, the first client has no way of knowing it has been downloaded.